Instruments and methods for manipulating a spinal fixation element

ABSTRACT

An instrument for manipulating a spinal fixation element relative to a bone anchor includes a bone anchor grasping mechanism, a first adjustment mechanism, and a second adjustment mechanism. The bone anchor grasping mechanism includes a first arm having a distal end configured to engage an opening provided in the bone anchor. The first adjustment mechanism includes a second arm pivotally connected to the first arm. The second arm has a distal end configured to engage an opening provided in the bone anchor and is operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm. The second adjustment mechanism is coupled to the bone anchor grasping mechanism or the first adjustment mechanism and is movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.

BACKGROUND

Spinal fixation systems may be used in orthopedic surgery to align and/or fix a desired relationship between adjacent vertebrae. Such systems typically include a spinal fixation element, such as a relatively rigid fixation rod or plate or a relatively flexible tether or cable, that is coupled to adjacent vertebrae by attaching the element to various anchoring devices, such as hooks, bolts, wires, or screws. The spinal fixation element can have a predetermined contour that has been designed according to the properties of the target implantation site, and once installed, the spinal fixation element holds the vertebrae in a desired spatial relationship, either until desired healing or spinal fusion has taken place, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of the vertebra. Since each vertebra varies in shape and size, a variety of anchoring devices have been developed to facilitate engagement of a particular portion of the bone. Pedicle screw assemblies, for example, have a shape and size that is configured to engage pedicle bone. Such screws typically include a threaded shank that is adapted to be threaded into a vertebra, and a head portion having a spinal fixation element receiving element, which, in spinal rod applications, is usually in the form of a U-shaped slot formed in the head for receiving the rod. A set-screw, plug, cap or similar type of closure mechanism, is used to lock the rod into the rod-receiving portion of the pedicle screw. In use, the shank portion of each screw is then threaded into a vertebra, and once properly positioned, a fixation rod is seated through the rod-receiving portion of each screw and the rod is locked in place by tightening a cap or similar type of closure mechanism to securely interconnect each screw and the fixation rod. Other anchoring devices also include hooks and other types of bone screws.

While current spinal fixation systems have proven effective, difficulties have been encountered in mounting rods, or other spinal fixation elements, into the rod-receiving portion of various fixation devices. In particular, it can be difficult to align and seat the rod into the rod receiving portion of adjacent fixation devices due to the positioning and rigidity of the vertebra into which the fixation device is mounted. Thus, the use of a spinal rod approximator, also referred to as a spinal rod reducer, is often required in order to grasp the head of the fixation device, and reduce the rod into the rod-receiving portion of the fixation device.

While several rod approximators are known in the art, some tend to be difficult and very time-consuming to use. Accordingly, there is a need for an improved rod approximator and methods for seating a spinal rod in a rod-receiving portion of one or more spinal implants.

SUMMARY

Disclosed herein are instruments and methods for manipulating a spinal fixation element, such as a spinal rod, relative to a bone anchor, such as a polyaxial or monoaxial bone screw. The instruments and methods disclosed herein are particularly suited for lateral and vertical alignment of a spinal fixation element relative to a bone anchor.

In accordance with one exemplary embodiment, an instrument for manipulating a spinal fixation element relative to a bone anchor may comprise a bone anchor grasping mechanism, a first adjustment mechanism and a second adjustment mechanism. In the exemplary embodiment, the bone anchor grasping mechanism may include a first arm having a distal end configured to engage an opening provided in the bone anchor. The first adjustment mechanism may include a second arm pivotally connected to the first arm. The second arm may have a distal end configured to engage an opening provided in the bone anchor and may be operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm. The second adjustment mechanism may be coupled to at least one of the bone anchor grasping mechanism and the first adjustment mechanism and may be movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.

In accordance with another exemplary embodiment, an instrument for manipulating a spinal fixation element relative to a bone anchor may comprise a first arm, a second arm pivotally connected to the first arm, and adjustment mechanism coupled to the first arm and the second arm. In the exemplary embodiment, the first arm may have a distal end having an arcuate projection for engaging a first arcuate groove provided in the bone anchor. The second arm may have a distal end having an arcuate projection for engaging a second arcuate groove provided in the bone anchor. The first arm and second arm may be pivotable about a pivot axis that intersects the first arm and second arm and the second arm may be operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm. The adjustment mechanism may be movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.

In accordance with another exemplary embodiment, an instrument for manipulating a spinal fixation element relative to a bone anchor may comprise a first arm, a second arm pivotally connected to the first arm, an adjustment mechanism coupled to first arm and the second arm, and a coupling mechanism connected to the first arm and the second arm. The first arm may have a distal end having a projection for engaging a first opening provided in the bone anchor and the second arm may have a distal end having a projection for engaging a second opening provided in the bone anchor. The first arm and second arm may be pivotable about a pivot axis that intersects the first arm and second arm and the second arm may be operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm. The adjustment mechanism may be movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor. The coupling mechanism may be positioned between the first arm and the second arm such that the pivot axis intersects the coupling mechanism. The coupling mechanism may be configured to receive the adjustment mechanism and permit motion of the adjustment mechanism relative to the first arm and the second arm.

BRIEF DESCRIPTION OF THE FIGURES

These and other features and advantages of the instruments and methods disclosed herein will be more fully understood by reference to the following detailed description in conjunction with the attached drawings in which like reference numerals refer to like elements through the different views. The drawings illustrate principles of the instruments and methods disclosed herein and, although not to scale, show relative dimensions.

FIG. 1 is an assembly view of an exemplary embodiment of an instrument for manipulating a spinal fixation element relative to a bone anchor;

FIG. 2 is a front view of the instrument of FIG. 1;

FIG. 3 is a side view of the instrument of FIG. 1;

FIG. 4 is a top perspective view of the instrument of FIG. 1;

FIG. 5 is a side view of the distal end of the instrument of FIG. 1;

FIG. 6 is a side view in cross section of the distal end of the instrument of FIG. 1;

FIG. 7 is a side view of another exemplary embodiment of an instrument for manipulating a spinal fixation element relative to a bone anchor;

FIG. 8 is a side view of another exemplary embodiment of an instrument for manipulating a spinal fixation element relative to a bone anchor, illustrating the lateral activation mechanism of the instrument;

FIG. 9 is a side view of another exemplary embodiment of an instrument for manipulating a spinal fixation element relative to a bone anchor, illustrating the coupling mechanism integrated into an arm of the instrument;

FIG. 10 is a side view of an alternative exemplary embodiment of a coupling mechanism configured to permit motion of the adjustment mechanism relative to the first arm and the second arm of the instrument;

FIGS. 11A-11C are side views of alternative exemplary embodiments of the distal end of the adjustment mechanism, illustrating alternative mechanisms for interacting with the spinal fixation element;

FIGS. 12A-12D are side views of alternative exemplary embodiments of the distal end of the first arm of the instrument, illustrating alternative bone anchor engagement mechanisms; and

FIG. 13 is a side view of the instrument of FIG. 1, illustrating the operation of the instrument to adjust a spinal fixation element relative to a bone anchor.

DETAIL DESCRIPTION OF EXEMPLARY EMBODIMENTS

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the instruments and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those of ordinary skill in the art will understand that the instruments and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention.

The articles “a” and “an” are used herein to refer to one or to more than one (i.e. to at least one) of the grammatical object of the article. By way of example, “an element” means one element or more than one element.

The terms “comprise,” “include,” and “have,” and the derivatives thereof, are used herein interchangeably as comprehensive, open-ended terms. For example, use of “comprising,” “including,” or “having” means that whatever element is comprised, had, or included, is not the only element encompassed by the subject of the clause that contains the verb.

FIGS. 1-6 and 13 illustrate an exemplary embodiment of an instrument 10 for manipulating a spinal fixation element 12, such as, for example, a spinal rod, a plate, a tether or cable or combinations thereof, relative to a bone anchor 14, such as, for example, a bone screw or hook. The exemplary instrument 10 is particularly suited adjust a spinal fixation element in two directions relative to a bone anchor. For example, the exemplary instrument 10 is suited for both lateral adjustment of the spinal fixation element 12 and vertical adjustment of the spinal fixation element 12 relative to the bone anchor 14. The exemplary instrument 10 includes a bone anchor grasping mechanism 18 configured to engage an opening in the bone anchor 14, a first adjustment mechanism 20 operable to adjust the spinal fixation element 12 in a first direction relative to the bone anchor 14 and a second adjustment mechanism 22 operable to adjust the spinal fixation element 10 in a second direction, at an angle to the first direction, e.g., perpendicular to the first direction, relative to the bone anchor 14.

As illustrated and in the description of the exemplary instrument 10 that follows the spinal fixation element is a spinal rod 12 and the bone anchor is a monoaxial bone screw 14. One skilled in the art will appreciate that the spinal fixation element and the bone anchor are not limited to the illustrated exemplary embodiments. The instrument may be used with any type of spinal fixation element and any type of bone anchor.

The bone anchor grasping mechanism 18 of the exemplary instrument 10 may include a first arm 24 having a distal end 26 configured to releasably engage a bone anchor. For example, the first arm 24 may be engaged to a bone anchor in a manner that allows the first arm 24, and thus the instrument 10, to be connected to the bone anchor 14 during use, e.g., during adjustment of the spinal fixation element 12 relative to the bone anchor 14, and allows the first arm 24, and thus, the instrument 10, to be disconnected from the bone anchor 14 at the conclusion of the procedure. Preferably, the first arm 24 can be disconnected remotely. For example, the exemplary embodiment, the first arm 24 can be disconnected from the bone anchor by manipulation of the proximal end of the first arm 24.

Referring to FIGS. 6, 12A and 12B, the distal end 26 of the first arm 24 may be configured to engage an opening provided in the bone anchor 14. For example, the distal end 26 of the first arm 24 may include one or more radially inward facing projection 28 that is sized and shaped to seat within an opening provided in a portion of the bone anchor. The size, shape and number of projections can be varied depending on, for example, the opening(s) provided on the bone anchor and type of connection desired. In the illustrated exemplary embodiment, for example, the projection 28 is generally arcuate in shape and has a cross section and a curvature that is complementary to an arcuate groove 30 provided in the spinal fixation element receiving member 32 of the exemplary bone anchor 14. Exemplary bone anchors having such features are described in U.S. patent application Ser. No. 10/738,286, filed Dec. 16, 2003, incorporated herein by reference. In particular, the projection 28 has a distal surface 36, a proximal surface 38, and a generally radially facing connecting surface 40 that spans between the distal surface 36 and the proximal surface 38, as shown in FIG. 12B. In the illustrated embodiment, the distal surface 36 is generally oriented perpendicular to the longitudinal axis L of the instrument 10 and the connecting surface 40 is generally oriented parallel to the longitudinal axis L of the instrument 10 and perpendicular to the distal surface 36. One or both of the proximal surface 38 and the distal surface 36 may be oriented at an angle other than perpendicular to the longitudinal axis L of the instrument 10. For example, the proximal surface 38 may be oriented at an angle A to an orthogonal line 80, which is oriented perpendicular to the longitudinal axis L of the instrument 10. In the exemplary embodiment, the angle A may be approximately 5° to approximately 30° and is preferably approximately 20°. The distal surface 36 and the proximal surface 38 may be oriented at the same angle or, as in the exemplary embodiment, may be oriented at different angles.

In alternative embodiments, the distal end 26 of the first arm 24 may include additional and/or alternatively positioned and/or shaped projections. For example, the distal end 26 of the first arm 24 may include a projection 28′ configured to engage a swaged opening positioned between the proximal and distal ends of the spinal fixation element receiving member 32 of the exemplary bone anchor 14, as illustrated in FIG. 12C. The projection 28′ may be generally cylindrical in shape, may be generally hemispherical in shape, or may have other suitable shapes. In alternative embodiments, the distal end 26 may include two projections, e.g., the arcuate projection 28 illustrated in FIGS. 12A and 12B and the projection 28′ illustrated in FIG. 12C. In alternative embodiments, the distal end 26 of the first arm 24 may not include a projection. For example, the distal end 26 may be sized and shaped to engage the distal end of the of the spinal fixation element receiving member 32 of the exemplary bone anchor 14, as illustrated in FIG. 12D.

Continuing to refer to FIGS. 1-6 and 13, in the exemplary instrument, the first adjustment mechanism 20 may include a second arm 50 that is pivotally connected to the first arm 24 and is operable to adjust the spinal fixation element 12 in a first direction upon pivoting of the second arm 50 relative to the first arm 24. For example, the first arm 24 may be directly pivotally connected to the second arm 50 such that the first arm 24 and the second arm 50 pivot about a pivot axis 52 that intersects the first arm 24 and the second arm 50. In alternative embodiments, the first arm 24 may be indirectly pivotally connected to the second arm 50, for example, the first arm 24 may be off set from the second arm 50 such that the first arm 24 and the second arm 50 pivot about a pivot axis that does not intersect both the first arm 24 and the second arm 50.

The second arm 50 may have a distal end 56 configured to releasably engage the bone anchor 14. The distal end 56 of the second arm 50 may be configured in a manner analogous to the distal end 26 of the first arm 24. For example, the distal end 56 of the second arm 50 may include a projection 58 sized and shape to engage an opening in the bone anchor 14.

The inner surface 60 of the second arm 50 of the exemplary instrument 10 may be configured to facilitate contact with and adjustment of the spinal fixation element 12 relative to the bone anchor. For example, the inner surface 60 of the second arm 50 may be coated with a material having a relatively low coefficient of friction to facilitate movement of the spinal fixation element 12 along the inner surface 60 of the second arm 50 during adjustment of the spinal fixation element in the first direction.

Continuing to refer to FIGS. 1-6 and 13, the second adjustment mechanism 22 may be coupled to the first arm 24 and/or the second arm 50 and may be movable relative to the first arm 24 and/or the second arm 50 to adjust the spinal fixation element 12 relative to the bone anchor 14 in a second direction that is different to, e.g., at an angle to, the first direction. In the illustrated embodiment, the second adjustment mechanism 22 comprises an elongated tubular body 60 having a proximal end 62 and a distal end 64 and a lumen 66 extending between the proximal end 62 and the distal end 64. The lumen 66 may be sized and shaped to permit a closure mechanism delivery instrument 90 to be positioned therethrough. The closure mechanism delivery instrument 90 is provided for the delivery of a closure mechanism 92, for example, a set screw or the like, to the bone anchor 14 to secure the spinal fixation element 12 relative to the bone anchor 12 after alignment of the spinal fixation element 12. In the illustrated embodiment, the closure mechanism delivery instrument 90 is a screwdriver having a distal end 94 with external threads for engaging the closure mechanism 92.

The distal end 64 of the tube 60 may indirectly or directly contact the spinal fixation element 12 to adjust the spinal fixation element 12 in the second direction. For example, in the illustrated embodiment, the tube 60 may be advanced with the closure mechanism delivery instrument 90 and the closure mechanism 92 may be positioned distal to the distal end 64 of the tube 60, as illustrated in FIGS. 11B and 13. In such embodiments, the closure mechanism 92 may contact the spinal fixation element 12 and, thus, the tube 60 may adjust the spinal fixation element 12 through the closure mechanism 92. In alternative embodiments, the distal end 64 of the tube 60 may directly contact the spinal fixation element 12 to effect adjustment of the spinal fixation element 12, as illustrated in FIG. 11C. In certain embodiments, the distal end 64 of the tube may be sized and shaped to facilitate contact with the spinal fixation element 12. For example, the distal end 64 may be forked or bifurcated to engage the spinal fixation element 12 on opposing sides, as illustrated in FIG. 11A. In such embodiments, the distal end 64 may have an arcuate contact surface 68 having a curvature approximate to the curvature of the spinal fixation element 12.

The exemplary instrument 10 may include a coupling mechanism 100 that is connected to the first arm 24 and/or the second arm 50 and is configured to receive the second adjustment mechanism 22, e.g., tube 60, and permit motion of the second adjustment mechanism 22 relative to the first arm 24 and/or the second arm 50. In the illustrated embodiment, for example, the coupling mechanism 100 is a collar or nut 102 having internal threads 104 that may engage external threads 70 provided on the tube 60 between the proximal end 62 and the distal end 64 of the tube 60. Rotation of the tube 60 relative to the collar 102 causes the tube 60 to advance distally or proximally, depending on the direction of rotation, relative to the first arm 24 and the second arm 50. The tube 60 may be provided with a handle 72 at the proximal end 62 of the tube 60 to facilitate gripping and rotation of the tune 60.

The collar 102 may be connected to the first arm 24 and/or the second arm 50 anywhere along the length of the arm(s). In the illustrated embodiment, for example, the collar 102 is connected to and positioned between the first arm 24 and the second arm 50. The collar 102 may be positioned between the proximal and distal ends of the first arm 24 and the second arm 50 proximate the area in which the arms intersect. In the illustrated embodiment, for example, the collar 102 is positioned such that the pivot axis 52 intersects the collar 102.

In alternative embodiments, the collar 102 may be integral to the first arm 24 and/or the second arm 50. Referring to FIG. 9, for example, the collar 102 may be integral to the second arm 50 of the instrument 10. Alternatively, the collar 102 may be integral to the first arm 24 or be formed by both the first arm 24 and the second arm 50.

In alternative embodiments, the collar 102 may be configured to allow the tube 60 to advance distally without rotation. For example, the collar 102 may include a threaded member 106 that is movable in a direction perpendicular to the tube 60 to allow the threaded member 106 to selectively engage the threads 70 on the tube 60, as illustrated in FIG. 10. In the illustrated embodiment, the threaded member 106 is movable between a first position in which the threaded member 106 engages the external threads 70 in the tube 60, as illustrated in FIG. 10, and a second position in which the threaded member 106 disengages the external threads 70 on the tube 60 to permit axial motion of the tube 60 without rotation. In this manner, the tube 60 may be quickly advanced, without the need for rotation, into contact with the spinal fixation element 12. Upon engagement with the spinal fixation element 12, the tube 60 may be rotated to engage the threaded 70 on the tube 60 with the threads of the threaded member 106 and, thus, further advance the spinal fixation element 12. The collar 106 may include one or more springs 108 that bias the threaded member 106 into engagement with the threads 70 of the tube 60, i.e., the first position. The teeth 110 of the threaded member 106 may include an angled flank 112 that facilitates translation of the threaded member 106 from the first position to the second position.

The exemplary instrument 10 may include an activation mechanism 120 coupled to the bone anchor grasping mechanism 18 and to the first adjustment mechanism 20 to effect relative motion of the first arm 24 and the second arm 50. For example, the activation mechanism 120 may comprise a first handle 122 connected and proximal to the first arm 24 and a second handle 124 connected and proximal to the second arm 50. The first handle 122 may be pivotally connected to the second handle 124. Motion of the first handle 122 and the second handle 124 towards one another causes the distal end 26 of the first arm 24 to move toward the distal end 56 of the second arm 50. The activation mechanism 120 may include a spring or the like positioned between the first handle 122 and the second handle 124 to bias the first handle 122 and the second handle 124 to an open, separated position. The activation mechanism 120 may also include a locking mechanism, such as a latch or a ratchet assembly, that is operable to lock the handles 122, 124 in position relative to one another, for example, in a closed position to retain the bone anchor between the distal ends 26, 56 of the arms 24, 50.

Although the exemplary activation mechanism 120 includes two handles 122, 124, in other exemplary embodiments, the activation mechanism 120 may include additional pivotally connected linkages to increase the mechanical advantage provided by the activation mechanism.

In the exemplary embodiment, the handles 122, 124 of the activation mechanism 120 are oriented generally in a direction parallel to the longitudinal axis L of the instrument 10. In alternative embodiments, the activation mechanism 120 may comprise a fixed handle 130 and a movable handle 132 that is pivotally connected to the fixed handle 130 at a pivot point 134 proximal to the pivot axis 52 of the first arm 24 and the second arm 50, as illustrated in FIG. 7. In the exemplary embodiment illustrated in FIG. 7, motion of the movable handle 132 toward the fixed handle 130 causes the causes the distal end 66 of the second arm 50 to move toward the distal end 26 of the first arm 24. The movable arm 132 may be connected to the second arm 50 by one or more pivotally connected linkages.

In alternative embodiments, the one or more of the handles of the activation mechanisms 120 may be laterally oriented relative to the longitudinal axis L of the instrument 10. Referring to FIG. 8, for example, a movable handle 132 and a fixed handle 130 may be oriented lateral to, e.g., at angle to, the longitudinal axis L of the instrument 10. In the embodiment illustrated in FIG. 8, for example, the movable handle 132 and the fixed handle 130 are oriented generally perpendicular to the longitudinal axis L of the instrument 10.

The components of the exemplary instrument 10 may be made from any material suitable for use in vivo, including, for example, metals such as stainless steel and titanium, polymers, or composites thereof. The components of the exemplary instrument 10 may be constructed of the same or different materials.

In use, the exemplary instrument 10 may be employed to adjust the position of a spinal fixation element 12 in multiple directions relative to a bone anchor. Referring to FIG. 13, the distal end 26 of the first arm 24 may be engaged with the bone anchor 14. By moving the second handle 122 toward the first handle 124, in the direction of arrow A, the distal end 56 of the second arm 50 is pivoted about the pivot axis 52 and moved in the direction of the distal end 26 of the first arm 24 and the bone anchor 14, as indicated by arrow B. As the second arm 50 moves toward the bone anchor 14, the inner surface 60 of the second arm 50 engages the spinal fixation element 12 to move the spinal fixation element 12 in a first direction, indicated by arrow C, toward the bone anchor 14. This is generally referred to as lateral approximation of the spinal fixation element 12.

Upon vertical alignment of the spinal fixation element 12 with the longitudinal axis L of the instrument and the bone anchor, the tube 60 may be advanced distally in a second direction into contact with spinal fixation element 12, as indicated by arrow D. Further advancement of the tube 60 toward the bone anchor 14 advances the spinal fixation element 12 toward the bone anchor 14 until the spinal fixation element 12 is seated in the bone anchor 14. The delivery instrument 90 may used to engage the closure mechanism 92 with the bone anchor 14 and secure the spinal fixation element 12 to the bone anchor 14.

While the instruments and methods of the present invention have been particularly shown and described with reference to the exemplary embodiments thereof, those of ordinary skill in the art will understand that various changes may be made in the form and details herein without departing from the spirit and scope of the present invention. Those of ordinary skill in the art will recognize or be able to ascertain many equivalents to the exemplary embodiments described specifically herein by using no more than routine experimentation. Such equivalents are intended to be encompassed by the scope of the present invention and the appended claims. 

1. An instrument for manipulating a spinal fixation element relative to a bone anchor, the instrument comprising: a bone anchor grasping mechanism including a first arm having a distal end configured to engage an opening provided in the bone anchor, a first adjustment mechanism including a second arm pivotally connected to the first arm, the second arm having a distal end configured to engage an opening provided in the bone anchor, the second arm being operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm, and a second adjustment mechanism coupled to at least one of the bone anchor grasping mechanism and the first adjustment mechanism, the second adjustment mechanism being movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.
 2. The instrument of claim 1, wherein the first arm is directly pivotally connected to the second arm, the first arm and second arm pivoting about a pivot axis that intersects the first and second arm.
 3. The instrument of claim 1, further comprising a coupling mechanism positioned between and connected to the first arm and the second arm, the coupling mechanism being configured to receive the second adjustment mechanism and permit motion of the second adjustment mechanism relative to the first arm.
 4. The instrument of claim 3, wherein the coupling mechanism is an internally threaded nut for engaging external threads provided on the second adjustment mechanism.
 5. The instrument of claim 4, wherein the first arm and second arm pivot about a pivot axis that intersects the first arm and second arm and the pivot axis intersects the coupling mechanism.
 6. The instrument of claim 4, wherein the coupling mechanism includes a thread section that is movable between a first position in which the thread section engages the external threads on the second adjustment mechanism and a second position in which the thread section disengages the external threads on the second adjustment mechanism to permit axial motion of the second adjustment mechanism relative to the first arm.
 7. The instrument of claim 1, wherein the distal end of the first arm includes a projection sized and shaped to releaseably engage the opening in the bone anchor.
 8. The instrument of claim 7, wherein the projection is generally arcuate in shape having a curvature approximate to a curvature of the opening in the bone anchor.
 9. The instrument of claim 8, wherein the projection has a distal surface, a proximal surface, and a connecting surface extending between the distal surface and the proximal surface.
 10. The instrument of claim 9, wherein the proximal surface is oriented at an angle other than perpendicular to a longitudinal axis of the instrument.
 11. The instrument of claim 1, further comprising an activation mechanism coupled to the bone anchor grasping mechanism and to the first adjustment mechanism to effect motion of the first arm relative to the second arm.
 12. The instrument of claim 11, wherein the activation mechanism comprises a first handle connected to the first arm and a second handle connected to the second arm.
 13. The instrument of claim 12, wherein the first handle and the second handle are oriented generally in a direction parallel to the longitudinal axis of the instrument.
 14. The instrument of claim 12, wherein at least one of the first handle and the second handle is oriented lateral to the longitudinal axis of the instrument.
 15. The instrument of claim 1, wherein the second adjustment mechanism is tubular in shape having a lumen extending therethrough.
 16. The instrument of claim 15, further comprising a delivery instrument for delivering a closure mechanism to the bone anchor, the delivery instrument being positionable through the second adjustment mechanism to deliver a closure mechanism to the bone anchor.
 17. An instrument for manipulating a spinal fixation element relative to a bone anchor, the instrument comprising: a first arm having a distal end having an arcuate projection for engaging a first arcuate groove provided in the bone anchor, a second arm pivotally connected to the first arm, the second arm having a distal end having an arcuate projection for engaging a second arcuate groove provided in the bone anchor, the first arm and second arm being pivotable about a pivot axis that intersects the first arm and second arm, the second arm being operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm, and an adjustment mechanism coupled to first arm and the second arm, the adjustment mechanism being movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor.
 18. The instrument of claim 17, further comprising a coupling mechanism positioned between and connected to the first arm and the second arm, the coupling mechanism being configured to receive the adjustment mechanism and permit motion of the adjustment mechanism relative to the first arm and the second arm.
 19. The instrument of claim 18, wherein the pivot axis intersects the coupling mechanism.
 20. An instrument for manipulating a spinal fixation element relative to a bone anchor, the instrument comprising: a first arm having a distal end having a projection for engaging a first opening provided in the bone anchor, a second arm pivotally connected to the first arm, the second arm having a distal end having a projection for engaging a second opening provided in the bone anchor, the first arm and second arm being pivotable about a pivot axis that intersects the first arm and second arm, the second arm being operable to adjust a spinal fixation element in a first direction upon pivoting relative to the first arm, an adjustment mechanism coupled to first arm and the second arm, the adjustment mechanism being movable relative to the bone anchor grasping mechanism to adjust the spinal fixation element in a second direction, perpendicular to the first direction, relative to the bone anchor, and a coupling mechanism connected to the first arm and the second arm and positioned between the first arm and the second arm such that the pivot axis intersects the coupling mechanism, the coupling mechanism being configured to receive the adjustment mechanism and permit motion of the adjustment mechanism relative to the first arm and the second arm. 